World Health Organization statistics show that breast cancer is the world's second cause of cancer deaths in women. Over the past few decades, the incidence of breast cancer showed an increasing trend. It is expected that by 2020, there will be more than 1.7 million new cases of breast cancer each year. By 2012, there are 1.67 million new cases of breast cancer worldwide, accounting for 25% of all new cases of cancer, wherein 883,000 cases are in developed countries and 794,000 cases are in developing countries. The growth rate of new cases of breast cancer in developing countries is slightly higher than that in developed countries. There are 522,000 cases of breast cancer deaths, ranking fifth in lethality rate in all cancers. In underdeveloped areas, the breast cancer causes 324,000 women deaths, accounting for 14.3% of all cases of cancer deaths, and is the most frequent lethal cancer. In developed areas, there are 198,000 cases of breast cancer deaths in women, accounting for 15.4% of all cases of cancer deaths, second only to lung cancer. Therefore, breast cancer is still one of the world's important health problems.
According to the international patent WO2003/062236, palbociclib is an inhibitory agent for cyclin-dependent kinases (CDKs) 4 and 6, which inhibits the synthesis of DNA primarily by preventing cells from G1 phase to S phase via the inhibition of CDK4/6 activity, and can be used to treat metastatic breast cancer. Clinical trial studies have shown that palbociclib combined with letrozole is very effective in postmenopausal patients with locally infiltrating breast cancer or in newly diagnosed estrogen receptor (ER)-positive and HER-2-negative patients. Its chemical structure is as follows:

The structure and preparation method of said compound and its salts have been described in the international patent WO2003/062236 and U.S. Pat. No. 6,936,612. The preparation methods of free bases and salts of various acids are also described in the international patent application WO2005/005426 and U.S. Pat. Nos. 7,345,171 and 7,863,278. According to the description in the international patent application WO2005/005426, the solubility of the palbociclib free base in water is poor, which leads to a low bioavailability and is disadvantageous for the absorption in human body. The free base has a strong adhesive property upon impact, and said adhesive property is related to the specific surface area of the particles, so its particle size must be controlled in a certain range. According to the international patent application WO2014128588, it is necessary to use an active pharmaceutical ingredient (API) of palbociclib free base having a larger particle size in order to improve the physichemical properties and the capacity to produce a formulation product. If the palbociclib free base is reacted with an acid to generate salts so as to increase the solubility, the salts have a poor solid nature and thereby are disadvantageous for being developed as a solid formulation, according to the reports in the previously known patents.
At the same time, palbociclib is an insoluble drug. At present, palbociclib has been approved for sale in the United States. According to the instructions for the approved product of palbociclib in the United States, one of seven patients has poor absorption upon administration of the palbociclib product. For these patients, the efficacy of said product will be relatively low. It is likely that the poor solubility of the drug causes the poor absorption in some patients. Thus, in the present, it is very necessary to further improve the dosage form of palbociclib so as to increase the dissolution rate and bioavailability thereof.